Hydrothermal synthesis of high-purity zeolite X from coal fly ash for heavy metal removal: Kinetic and isotherm analysis

Abstract

Treated fly ash (TCFA) yielded high-purity, single-phase zeolite-X, efficiently removing Ni and V ions from aqueous solutions. The pretreatment process of raw fly ash (RCFA) involved magnetic fraction separation, followed by acid washing. Zeolites were synthesized by the fusion prior step to the hydrothermal treatment method. The VSM test shows that the MS value dropped from 2.19 to 1.43 emu/g due to removing the magnetic fraction. These findings align with XRF results showing a 98 % reduction in Fe2O3 content, while acid washing lowered other metal oxide content to below 12 %. XRD results indicate the successful synthesis of high-crystallinity, single-phase zeolite X-TCFA, achieved at 90 °C for 12 h. SEM images further confirm the purity of the product, revealing pyramidal octahedral-shaped single crystals. Additionally, BET analysis shows a high surface area of 452 m2/g, featuring mesopores from 2 to 50 nm. The FTIR spectrum displayed the characteristic peaks of Zeolite X, confirming the success of the preparation process. TCFA-zeolite X has high thermal stability based on TGA analysis. The pseudo-second-order model fits the kinetic data, suggesting that chemical adsorption mechanisms control Ni and V adsorption. Langmuir isotherm best-explained results, with max adsorption of 41.55 mg/g Ni and 32.38 mg/g V.